Computing devices, such as notebook computers, personal digital assistants, mobile communication devices, portable entertainment devices (e.g., handheld video game devices, multimedia players), and set-top-boxes (e.g., digital cable boxes, digital video disc (DVD) players) may include user interface devices that facilitate interaction between a user and the computing device.
One type of user interface device that has become more common operates by way of capacitance sensing. A capacitance sensing system may include a touchscreen, touch-sensor pad, a touch-sensor slider, or touch-sensor buttons, and may include an array of one or more capacitive sensor elements. Capacitive sensing typically involves measuring, through sensor signals, a change in capacitance associated with the capacitive sensor elements to determine a presence of a conductive object relative to the capacitive sensor elements. The measured changes in capacitance may be used to calculate a position of the conductive object. The conductive object may be, for example, a stylus or a user's finger.
When sensor elements are expected to provide the same signal response to equivalent inputs, signal variation due to variation in system gain level may be considered signal error. Sensor signals may also include error due to noise (e.g., electrical noise). Presence detection and position calculation that are in error may result when they are based on sensor signals that are in error.